GCQ(3) | Library Functions Manual | GCQ(3)

# NAME

GCQ_INIT, GCQ_INIT_HEAD, gcq_init, gcq_init_head, gcq_q, gcq_hq, gcq_head, gcq_remove, gcq_onlist, gcq_empty, gcq_linked, gcq_insert_after, gcq_insert_before, gcq_insert_head, gcq_insert_tail, gcq_tie, gcq_tie_after, gcq_tie_before, gcq_merge, gcq_merge_head, gcq_merge_tail, gcq_clear, gcq_remove_all, GCQ_ITEM, GCQ_GOT_FIRST, GCQ_GOT_LAST, GCQ_GOT_NEXT, GCQ_GOT_PREV, GCQ_DEQUEUED_FIRST, GCQ_DEQUEUED_LAST, GCQ_DEQUEUED_NEXT, GCQ_DEQUEUED_PREV, GCQ_GOT_FIRST_TYPED, GCQ_GOT_LAST_TYPED, GCQ_GOT_NEXT_TYPED, GCQ_GOT_PREV_TYPED, GCQ_DEQUEUED_FIRST_TYPED, GCQ_DEQUEUED_LAST_TYPED, GCQ_DEQUEUED_NEXT_TYPED, GCQ_DEQUEUED_PREV_TYPED, GCQ_GOT_FIRST_COND, GCQ_GOT_LAST_COND, GCQ_GOT_NEXT_COND, GCQ_GOT_PREV_COND, GCQ_DEQUEUED_FIRST_COND, GCQ_DEQUEUED_LAST_COND, GCQ_DEQUEUED_NEXT_COND, GCQ_DEQUEUED_PREV_COND, GCQ_GOT_FIRST_COND_TYPED, GCQ_GOT_LAST_COND_TYPED, GCQ_GOT_NEXT_COND_TYPED, GCQ_GOT_PREV_COND_TYPED, GCQ_DEQUEUED_FIRST_COND_TYPED, GCQ_DEQUEUED_LAST_COND_TYPED, GCQ_DEQUEUED_NEXT_COND_TYPED, GCQ_DEQUEUED_PREV_COND_TYPED, GCQ_FOREACH, GCQ_FOREACH_REV, GCQ_FOREACH_NVAR, GCQ_FOREACH_NVAR_REV, GCQ_FOREACH_RO, GCQ_FOREACH_RO_REV, GCQ_FOREACH_DEQUEUED, GCQ_FOREACH_DEQUEUED_REV, GCQ_FOREACH_TYPED, GCQ_FOREACH_REV_TYPED, GCQ_FOREACH_NVAR_TYPED, GCQ_FOREACH_NVAR_REV_TYPED, GCQ_FOREACH_RO_TYPED, GCQ_FOREACH_RO_REV_TYPED, GCQ_FOREACH_DEQUEUED_TYPED, GCQ_FOREACH_DEQUEUED_REV_TYPED, GCQ_FIND, GCQ_FIND_REV, GCQ_FIND_TYPED, GCQ_FIND_REV_TYPED — Generic Circular Queues

# SYNOPSIS

#include <sys/gcq.h>

struct gcq;
struct gcq_head;

GCQ_INIT(name);

GCQ_INIT_HEAD(name);

static inline void
gcq_init(struct gcq *q);

static inline void
gcq_init_head(struct gcq_head *head);

static inline struct gcq *
gcq_q(struct gcq_head *head);

static inline struct gcq *
gcq_hq(struct gcq_head *head);

static inline struct gcq_head *
gcq_head(struct gcq *q);

static inline struct gcq *
gcq_remove(struct gcq *q);

static inline bool
gcq_onlist(struct gcq *q);

static inline bool
gcq_empty(struct gcq_head *head);

static inline bool
gcq_linked(struct gcq *prev, struct gcq *next);

static inline void
gcq_insert_after(struct gcq *on, struct gcq *off);

static inline void
gcq_insert_before(struct gcq *on, struct gcq *off);

static inline void
gcq_insert_head(struct gcq_head *head, struct gcq *q);

static inline void
gcq_insert_tail(struct gcq_head *head, struct gcq *q);

static inline void
gcq_tie(struct gcq *dst, struct gcq *src);

static inline void
gcq_tie_after(struct gcq *dst, struct gcq *src);

static inline void
gcq_tie_before(struct gcq *dst, struct gcq *src);

static inline void
gcq_merge(struct gcq *dst, struct gcq *src);

static inline void
gcq_merge_tail(struct gcq_head *dst, struct gcq_head *src);

static inline void
gcq_merge_head(struct gcq_head *dst, struct gcq_head *src);

static inline void
gcq_clear(struct gcq *q);

static inline void
gcq_remove_all(struct gcq_head *head);

type *
GCQ_ITEM(q, type, name);

bool
GCQ_GOT_FIRST(var, head);

bool
GCQ_GOT_LAST(var, head);

bool
GCQ_GOT_NEXT(var, current, head, start);

bool
GCQ_GOT_PREV(var, current, head, start);

bool
GCQ_DEQUEUED_FIRST(var, head);

bool
GCQ_DEQUEUED_LAST(var, head);

bool
GCQ_DEQUEUED_NEXT(var, current, head, start);

bool
GCQ_DEQUEUED_PREV(var, current, head, start);

bool
GCQ_GOT_FIRST_TYPED(tvar, head, type, name);

bool
GCQ_GOT_LAST_TYPED(tvar, head, type, name);

bool
GCQ_GOT_NEXT_TYPED(tvar, current, head, start, type, name);

bool
GCQ_GOT_PREV_TYPED(tvar, current, head, start, type, name);

bool
GCQ_DEQUEUED_FIRST_TYPED(tvar, head, type, name);

bool
GCQ_DEQUEUED_LAST_TYPED(tvar, head, type, name);

bool
GCQ_DEQUEUED_NEXT_TYPED(tvar, current, head, start, type, name);

bool
GCQ_DEQUEUED_PREV_TYPED(tvar, current, head, start, type, name);

bool
GCQ_GOT_FIRST_COND(var, head, cond);

bool
GCQ_GOT_LAST_COND(var, head, cond);

bool
GCQ_GOT_NEXT_COND(var, current, head, start, cond);

bool
GCQ_GOT_PREV_COND(var, current, head, start, cond);

bool
GCQ_DEQUEUED_FIRST_COND(var, head, cond);

bool
GCQ_DEQUEUED_LAST_COND(var, head, cond);

bool
GCQ_DEQUEUED_NEXT_COND(var, current, head, start, cond);

bool
GCQ_DEQUEUED_PREV_COND(var, current, head, start, cond);

bool
GCQ_GOT_FIRST_COND_TYPED(tvar, head, type, name, cond);

bool
GCQ_GOT_LAST_COND_TYPED(tvar, head, type, name, cond);

bool
GCQ_GOT_NEXT_COND_TYPED(tvar, current, head, start, type, name, cond);

bool
GCQ_GOT_PREV_COND_TYPED(tvar, current, head, start, type, name, cond);

bool
GCQ_DEQUEUED_FIRST_COND_TYPED(tvar, head, type, name, cond);

bool
GCQ_DEQUEUED_LAST_COND_TYPED(tvar, head, type, name, cond);

bool
GCQ_DEQUEUED_NEXT_COND_TYPED(tvar, current, head, start, type, name, cond);

bool
GCQ_DEQUEUED_PREV_COND_TYPED(tvar, current, head, start, type, name, cond);

GCQ_FOREACH(var, head);

GCQ_FOREACH_REV(var, head);

GCQ_FOREACH_NVAR(var, nvar, head);

GCQ_FOREACH_NVAR_REV(var, nvar, head);

GCQ_FOREACH_RO(var, nvar, head);

GCQ_FOREACH_RO_REV(var, nvar, head);

GCQ_FOREACH_DEQUEUED(var, nvar, head);

GCQ_FOREACH_DEQUEUED_REV(var, nvar, head);

GCQ_FOREACH_TYPED(var, head, tvar, type, name);

GCQ_FOREACH_REV_TYPED(var, head, tvar, type, name);

GCQ_FOREACH_NVAR_TYPED(var, nvar, head, tvar, type, name);

GCQ_FOREACH_NVAR_REV_TYPED(var, nvar, head, tvar, type, name);

GCQ_FOREACH_RO_TYPED(var, nvar, head, tvar, type, name);

GCQ_FOREACH_RO_REV_TYPED(var, nvar, head, tvar, type, name);

GCQ_FOREACH_DEQUEUED_TYPED(var, nvar, head, tvar, type, name);

GCQ_FOREACH_DEQUEUED_REV_TYPED(var, nvar, head, tvar, type, name);

GCQ_FIND(var, head, cond);

GCQ_FIND_REV(var, head, cond);

GCQ_FIND_TYPED(var, head, tvar, type, name, cond);

GCQ_FIND_REV_TYPED(var, head, tvar, type, name, cond);

GCQ_ASSERT(cond);

# DESCRIPTION

The generic circular queue is a doubly linked list designed for efficient merge operations and unconditional removal. All basic operations can be performed with or without use of a separate head, allowing easy replacement of any pointers where efficient removal is desired. The meaning of the data type will not change; direct use and defined operations can be mixed when convenient. The basic type is:

    struct gcq {
    	struct gcq *q_next;
    	struct gcq *q_prev;
    };

The structure must first be initialized such that the q_next and q_prev members point to the beginning of the struct gcq. This can be done with gcq_init() and gcq_init_head() or with constant initializers GCQ_INIT() and GCQ_INIT_HEAD(). A struct gcq should never be given NULL values.

The structure containing the struct gcq can be retrieved by pointer arithmetic in the GCQ_ITEM() macro. List traversal normally requires knowledge of the list head to safely retrieve list items.

Capitalized operation names are macros and should be assumed to cause multiple evaluation of arguments. `TYPED` variants of macros set a typed pointer variable instead of or in addition to struct gcq * arguments. Additional type specific inlines and macros around some GCQ operations can be useful.

A few assertions are provided when DIAGNOSTIC is defined in the kernel or _DIAGNOSTIC is defined in userland. If GCQ_USE_ASSERT is defined prior to header inclusions then assert() will be used for assertions and NDEBUG can be used to turn them off. GCQ_ASSERT() is a wrapper around the used assertion function. None of the operations accept NULL arguments, however this is not tested by assertion.

The head is separately named for type checking but contains only a struct gcq, a pointer to which can be retrieved via gcq_hq(). The reverse operation is performed by gcq_head(), turning the supplied struct gcq * into struct gcq_head *. gcq_q() returns its struct gcq * argument and is used for type checking in GCQ_ITEM(). There are no functions for retrieving the raw q_prev and q_next pointers as these are usually clearer when used directly (if at all).

gcq_remove() returns the element removed and is always a valid operation after initialization. gcq_onlist() returns false if the structure links to itself and true otherwise. gcq_empty() is the negation of this operation performed on a head. gcq_linked() tests if `prev->q_next == next && next->q_prev == prev`.

gcq_tie() ties src after dst such that that if the old lists are DST, DST2 and SRC, SRC2, the new list is DST, SRC, SRC2, DST2. If dst and src are on the same list then any elements between but not including dst and src are cut from the list. If `dst == src` then the result is the same as gcq_remove(). gcq_tie() is equivalent to gcq_tie_after() except that the latter must only be used with arguments on separate lists or not on lists and asserts that `src != dst && dst->q_prev != src`. gcq_tie_before() performs the same operation on `dst->q_prev`.

gcq_merge() moves any elements on list src (but not src itself) to list dst. It is normally used with two heads via gcq_merge_head() or gcq_merge_tail(). If GCQ_UNCONDITIONAL_MERGE is defined prior to header inclusion then the merge operations will always perform a tie then remove src from the new list, which may reduce code size slightly.

gcq_clear() initializes all elements currently linked with q and is normally used with a head as gcq_remove_all().

gcq_insert_after() and gcq_insert_before() are slightly optimized versions of gcq_tie() for the case where off is not on a list and include assertions to this effect, which are also useful to detect missing initialization. gcq_insert_head() and gcq_insert_tail() are the same operations applied to a head.

GCQ_GOT_FIRST() and GCQ_GOT_LAST() set var to a pointer to the first or last struct gcq in the list or NULL if the list is empty and return false if empty and true otherwise. The boolean return is to emphasise that it is not normally safe and useful to directly pass the raw first/next/etc. pointer to another function. The macros are written such that the NULL values will be optimized out if not otherwise used. `DEQUEUED` variants also remove the member from the list. `COND` variants take an additional condition that is evaluated when the macro would otherwise return true. If the condition is false var or tvar is set to NULL and no dequeue is performed.

GCQ_GOT_NEXT() and variants take pointers to the current position, list head, and starting point as arguments. The list head will be skipped when it is reached unless it is equal to the starting point; upon reaching the starting point var will be set to NULL and the macro will return false. The next and prev macros also assert that current is on the list unless it is equal to start. These macros are the only provided method for iterating through the list from an arbitrary point. Traversal macros are only provided for list heads, however gcq_head() can be used to treat any item as a head.

Foreach variants contain an embedded `for` statement for iterating over a list. Those containing `REV` use the q_prev pointer for traversal, others use q_next. The plain GCQ_FOREACH() uses a single variable. `NVAR` variants save the next pointer at the top of the loop so that the current element can be removed without adjusting var. This is useful when var is passed to a function that might remove it but will not otherwise modify the list. When the head is reached both var and nvar elements are left pointing to the list head. `FOREACH` asserts that var, and `NVAR` asserts that nvar does not point to itself when starting the next loop. This assertion takes place after the variable is tested against the head so it is safe to remove all elements from the list. `RO` variants also set nvar but assert that the two variables are linked at the end of each iteration. This is useful when calling a function that is not supposed to remove the element passed. `DEQUEUED` variants are like `NVAR` but remove each element before the code block is executed. `TYPED` variants are equivalent to the untyped versions except that they take three extra arguments: a typed pointer, the type name, and the member name of the struct gcq used in this list. tvar is set to NULL when the head is reached.

GCQ_FIND() is a foreach loop that does nothing except break when the supplied condition is true. `REV` and `TYPED` variants are available.

# SEE ALSO

gcc(1), _DIAGASSERT(3), assert(3), queue(3), KASSERT(9)

# HISTORY

GCQ appeared in NetBSD 5.0.

May 1, 2007 | NetBSD 7.2